rabezzana



Sept- 19, 1933. H. RABEZZANA CENTER WIRE SCREW ASSEMBLY FOR RADIO PLUGS Filed Aug. '7, 1950 z w W m Patente d sept, 19, 193

(CENTER EJE SCREW SSEll llllt Html@ PLUGS lilector Rabemana, Flint, T/liich., assigner to il CG Spark Plug Company, lilint, lt/licli.,a a company of Michigan Application ture of these plugs the `electrode is cemented in the insulator core and it has been found that it is necessary to exercise a great deal of care in. the cementing. operation. This cement, which is injected into the bore in a wet or plastic state,

must be given suincient time, usually several days,

to thoroughly dry out and become set, and since the resistance element i prefer to use is more or less porous, it sometimes becomes permeated or partly saturated with the cement which affects and changes the characteristics of the resistance element, such change varying with the extent of saturation and making diicult a uniformity of Vproduct without proper precaution being tairen.

To provide an improved method of cementing and assembling the electrode in the insuiator, which will allow the cement to set more quickly and thereby eliminate excessive absorption ci cement by the resistance element, and result in a more uniform product so as to render more feasible large quantity production of plugs of the sort with the use of unskilled labor, and to further improve the structure of the plug, particularly from a manufacturing standpoint, are among the objects of the present invention.

To this end there is contemplated in a preferred, but not necessarily tlie only embodiment of the invention, the provision of a central electrode having an intermediate resistanceyelement with end wires projecting from opposite ends thereof, which may be inserted in the bore of the insulator and secured by cement that is injected in two steps with a suitable drying interval therebetween, the outer electrode wire being subsequently welded or otherwise secured to a binding post which closes the outer end of the bore after the last cement injection. By the two-step cement injection the resistance element is covered or surrounded by the wet cement at the first in- 0 jection but at this time the end of the bore is not closed by the binding post and the. relatively small quantity of cement adjacent the resistance element, is therefore directly exposed to the outside air. Because of this and since there is only a slight amount of cement involved the cement August l, M9369., Serial Noe Jili 5 iClaims. (CCH, 12S-169) can dry out more quickly and before any appreciable amount of it is taken up or absorbed by the material forming the resistance element.

'The invention will be better understood upon reference to the accompanying drawing where- M Figure l is a vertical sectional view showing the central electrode imbedded in the bore of an insulator after the first stage of cement injection.

Figure 2 is a sectional view alter the second stage of injection, and

yFigure 3 is a fragmentary sectional view of the upper end of a completed assembly.

Referring to the drawing, the central electrode is shown as consisting of an intermediate resistance element l which may be a stick of carbon, or the like, having affixed on its opposite ends as by means of cap pieces 2 and 3 respectively, electrode wires d and 5. These wires may be secured to the cap pieces by having enlargements or heads formed on their inner ends by an upsetting operation and the cap pieces in turn are secured to the resistance element by contracting or pinching inwardly the side wall or flanges thereof. The electrode is rst inserted in the insulator core 7, the bore of which is of reduced diameter at its inner end, as at e, to receive the inner wire 5 and slightly enlarged, as at 9, to receive the resistance element with the outer end thereof preferably screw threaded, as at l0. With the centrai electrode inserted in the borethe inner end of the insulator may then be placed over the nozale of a suitable cement injection machine for the injection of the plastic cementitious material l2 through the lower end of the bore and 'upwardly around the wire 5 and resistance element l until the resistance element is completelyy covered, as shown in Figure l. The parts thus assembled are then preferably placed in a suitable drying oven to set the cement.

I After a sufficient interval has elapsed to allow the cement l2 to set, a second charge of the cementitious material 13 is injected into the upper end of the bore and a hollow binding post l5 which, as shown in the drawing, is threaded from opposite ends with an intermediate flange or enlargement 16, is positioned over the electrode wire d and inserted into the wet cement in the upper end of the bore. rlhis insertion may taire place by inter-engaging the screw threads lo with the threads of the binding lpost and screwing the post down into the wet cement until the collar 16 engages the top of the insulator core, a pac ing gasket or ring 17 preferably being interposed between the collar and core. 'lhe engagement of the screw threads is preferably a sloppy one in order that the cement illling the loose spaces will lock the binding post in position. The as sembly is once again placed in the drying oven to set the cement last injected. Either before or after the last drying operation the wire 4 and binding post 15 are secured together as by means of a welded joint 18 shown in'Figure 3.

A metal jacket or shell, indicated by the dotted lines in Figure 2V, is later tted to the insulator core by means of which the spark plug is inserted in the combustion chamber of an engine in the usual fashion. This shell may carry an electrode grounded through the shell and engine and projected in spaced relation with the end of the wire 5 to form a spark gap across which the current may Hash when the plug is in use'and the ignition wiring connected to the binding post in the conn ventional manner. The use oi.' the resistance element 1 serves to reduce radio interference by damping the oscillations in the ignition circuit which usually follow the passage of current across the spark gap.

The structure described provides a spark plug with a resistance element built in as a part thereof and a method of assembling the partahas been found to be very eiiective for high quantity production inasmuch as there is no particular skill required of the operator. Y, By the two step injection of cement the driving out of the moisture in the cement is very much simplified and it has been found further that the characteristics of the resistance element oi' plugs, assembled in this manner, are not materially affected and that their 'action in use are more nearly uniform.

I claim:

1. In a spark plug, an insulator core, a hollow binding post at the outer end of the core, a sectional electrode including as a unitary assembly a porous intermediate section and a pair of end sections projecting from opposite ends of the porous section, and fixing cement surrounding neat/,2er

the porous section to hold the electrode in place, one of said end portions projecting beyond the cement and through the hollow post to enable ready connection between the post and porous section after the cement has set and a welded joint between the post and said projecting section.

2. In a spark plug, an insulator core, a sectional electrode Within the core including a porous intermediate section, and a pair of end sections projecting from opposite ends of the porous section and beyond the opposite ends of the core, ilxing cement surrounding the porous section to hold the electrode in the core, and a binding post adapted for mounting at one end of the core after the cement is set and provided with a hollow portion to receive the adjacent projecting end of the electrode for electrical connection therewith.

3. In a spark plug, an insulator core, an elec* trode section of porous material, fixing cement securing said section in the core, a binding post at the outer end of the core, and an electrode sec tion connecting the post with the rst mentioned electrode section and'being initially assembled as a unit with said section and projected beyond the cement to facilitate connection with the post after said cement has set.

4. In a spark plug, an insulator core, a center electrode projecting beyond opposite ends of the core, xing cement securing the electrode in place, a hollow binding post mounted on the outer end of the core independently of the cement which holds the electrode and adapted to receive the adjacent projecting end of the electrode, and means to electrically connect the post and electrode.

5. In a spark plug, an insulator core, a center electrode projecting beyond opposite ends of the core, xing cement securing the electrode in place, a hollow binding post associated with the outer end of the core and to receive the adjacent end of electrode and means for securing the electrode and post in electrical connection.

HECTOR RABEZZANA.

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